1. Technical Field
The present disclosure relates to relay networks and, more specifically, to virtual space-time code for relay networks.
2. Discussion of the Related Art
Multiple-Input and Multiple-Output (MIMO) relates to techniques for increasing radio communication performance with the use of multiple antennas. By employing MIMO techniques, data throughput and link range may be increased without additional bandwidth or transmit power.
MIMO techniques have been applied to various wireless technologies including cellular networks and Wireless Municipal Area Networks (WMAN) otherwise known as WiMAX. Examples of WiMAX technologies include networks adhering to IEEE 802.16 standards such as IEEE 802.16e mobile WiMAX standards.
In such MIMO systems, Space-Time Block Coding (STBC) is a technique used to transmit multiple copies of a data stream across multiple antennas. As multiple versions of the same data are received, the reliability of data transfer is increased. Accordingly, the error rate of data transmitted using STBC may be substantially lower than for conventionally transmitted data. STBC may be used in systems with multiple transmit antennas even where only a single receiving antenna is used.
A fundamental example of STBC employs the transmission of data correlated in an Alamouti fashion.
  C  =      [                            a                          b                                                  -                          b              *                                                            a            *                                ]  where the rows of the matrix represent time slots and the columns of the matrix represent transmission antennas. The data being transmitted is represented as “a” and “b.” The asterisk represents the complex conjugate. Thus in the first time slot, the first antenna transmits “a” and the second antenna transmits “b.” Then in the second time slot, the first antenna transmits “−b*” and the second antenna transmits “a*.”
Higher-order STBCs are used, however, Alamouti correlation is offered as a simple example, and the present disclosure may be described in terms of this example. It should be understood, however, that other STBC techniques may be used.
Much of the wireless network hardware presently in use, including base stations and relay stations, are not configured for MIMO transmission. Thus, many such base stations and relay stations have only a single transmission antenna. Accordingly, MIMO techniques are not utilized by a large number of existing wireless network hardware.